PG&E spokeswoman Brittany Chord said that testing, first scheduled to begin last Tuesday, was delayed partly because the utility did not want to interrupt residents during Memorial Day weekend at Ardenwood Park, which is near one end of the pipeline.

“We also wanted to make sure we were doing all we can to inform residents about the work we’re doing,” Chord said.

The one-mile section of pipeline was installed in 1949 and is 2 feet in diameter. It runs through the center of the city, between the corner of Cedar Boulevard and Lafayette Avenue and the corner of Cardiff Street and Jarvis Avenue, west of the Lake district.

Crews have begun preparation work at those intersections by digging a 10-by-25-foot pit to access the pipe.

On Tuesday, the utility performed the “venting” process, which starts by shutting down the valves on the section of pipe that’s being tested, and finishes by opening up that section to release natural gas into the air, Chord said.

To complete the eight-hour pressure-testing process, crews then will:

Fill a section of the pipe with 100,000 gallons of water.

Let the pipe sit for 24 hours to ensure that all the air is out.

Pressurize the water.

Hold that pressure for about eight hours.

Evacuate all the water out of the pipe.

Filter the water through charcoal.

Dry out the pipe with a “pig,” a device used to dry the pipe by pulling it through to absorb any remaining moisture.

Reattach the pipe and, lastly, redirect gas back into the pipe.

PG&E is testing about 150 miles of aging pipelines with traits similar to those in San Bruno, where a pipeline explosion in September killed eight people, destroyed 38 homes and left 17 other residences uninhabitable.

Pressure-testing in Hayward is scheduled to begin in mid-June, Chord said.

To inform residents about testing details, PG&E has scheduled an open house in Hayward from 5:30 to 7:30 p.m. Wednesday at La Quinta Inn, 20777 Hesperian Blvd.